New study reveals when West Antarctica’s largest glacier started retreating
BRITISH ANTARCTIC SURVEY

Reporting this week (Wednesday Nov. 23) in the journal Nature an international team led by British Antarctic Survey (BAS) explains that present-day thinning and retreat of Pine Island Glacier, one of the largest and fastest shrinking glaciers of the West Antarctic Ice Sheet, is part of a climate trend that was already underway as early as the 1940s.

It is already known that Pine Island Glacier — roughly two-thirds the size of the UK — has been thinning and retreating at an alarming rate since 1992 when satellite observations first started. The ice lost from this glacier and its neighbours, has added significantly to sea-level rise, and currently this area is one of biggest single unknowns in future projections. Until now, it was not known when the retreat of Pine Island Glacier started, or its underlying cause.

In this study, seabed sediment cores obtained from beneath the floating part of Pine Island Glacier have revealed that a cavity started to form beneath the shelf prior to the mid-1940s. This allowed warm sea water to flow under the shelf, and cause it to lift-off from a prominent sea-floor ridge which held it in place. This strongly suggests that current retreat was initiated by strong warming of the region associated with El Niño activity.

Lead author, marine geologist Dr James Smith from British Antarctic Survey, says:

‘We are very excited about this new finding as it provides the first direct evidence of the timing of glacier retreat even before we had satellites to measure them. The sediment cores were obtained through a 450-m deep hole in of ice, and up to 500 m of ocean. The sediment reveals climate events that initiated the current thinning of Pine Island Glacier. They show us how changes half-way across the planet in the tropical Pacific, reached through the ocean to influence the Antarctic ice sheet.

“Pine Island Glacier is one of the most inhospitable and remote areas of Antarctica, so to get all the equipment needed to hot-water drill through the ice shelf required a major effort from our collaborators at the US Antarctic Programme. On the ground it was real team effort to lower the drill by hand to the seabed on nearly 1000 m of rope. After all that work, the cores show us something so unexpected.”

‘A significant implication of our findings is that once an ice sheet retreat is set in motion it can continue for decades, even if what started gets no worse. It is possible that the changes we see today on Pine Island Glacier were essentially set in motion in the 1940s’.

Professor David Vaughan, co-author and Director of Science at British Antarctic Survey, says:

“Ice loss from this part of West Antarctica is already making a very significant contribution to global sea level rise, and is actually one of the largest uncertainties in global sea-level predictions. Understanding what initiated the current changes is one major piece of the jigsaw, and now we are already looking for the next — how long will these changes continue and how much ice will Pine Island Glacier and its neighbours lose in the coming century? Data from the UK science programme iSTAR will tell us even more about Pine Island Glacier, but these are big questions that need the international science community to work together.”

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A new joint programme recently announced by the UK Natural Environment Research Council (NERC) and the US National Science Foundation will allow a more focussed study of Pine Island Glacier and provide a new opportunity to understand West Antarctica and quantify how much sea level rise it might cause in the coming century .

5 thoughts on “Oops… West Antarctic ice sheet melting as far back as 1940s”

‘A significant implication of our findings is that once an ice sheet retreat is set in motion it can continue for decades, even if what started gets no worse. It is possible that the changes we see today on Pine Island Glacier were essentially set in motion in the 1940s’.

Just let that sink in, and regurgitate it every time someone mentions shrinking glaciers….

The retreat of Antarctic ice shelves is nothing new according to research published in the journal Geology by scientists from Universities of Durham, Edinburgh and British Antarctic Survey (BAS). (24 Feb, 2005)

A study of George VI Ice Shelf on the Antarctic Peninsula is the first to show that this currently ‘healthy’ ice shelf experienced an extensive retreat about 9500 years ago, more than anything seen in recent years. The retreat coincided with a shift in ocean currents that occurred after a long period of warmth.

The findings are particularly relevant for other studies on the West Antarctic Ice Sheet where scientists have found that a relatively warm current, Circumpolar Deep Water, is causing high melt rates on the underside of an ice shelf in Pine Island Bay.

This is some of the first evidence that a shift in ocean currents can actually destroy ice shelves.

In this case it’s possible that a preceding warm period may have primed the ice shelf to disintegrate when the ocean currents shifted.’

It is important to appreciate that ice shelf collapses have happened before.

For example, BAS scientists Carol Pudsey and Jeff Evans reported that the Prince Gustav Ice Shelf, which collapsed in 1995, had also collapsed several thousand years ago.

“Pine Island Glacier is nearly two-thirds the size of the UK or the size of Texas. So what’s the cause since CO2 was only around 310 ppm in the 1940s?”
Texas is 288,581 sq. mi.
UK is 93,628 sq. mi.
Pine Island Glacier is 68,000 sq. mi. or about the size of Florida.